Envy in a child worries us. It is so shameful and corrosive. Yet I confess to experiencing it on the rare occasions when I visit an independent school.

“Surely all children should have facilities like this?” I ask myself in the 10 minutes it takes to drive from the “porter’s lodge” to the main reception. And then the fees they charge - often five or six times the amount we spend per pupil in inner-city state schools. In short, envy turns to anger very quickly.

When the case for the abolition of public schools was abandoned in the 1960s, I joined in the debate about their charitable status. I have cooperated, notably through the Southwark Schools Partnership, started under the London Challenge to try to gain some crumbs from the rich people’s table.

Recently my “sleeping dog” attitude to this has been disturbed. Did you know that public schools have been cloning themselves in the Middle East and Far East? Step forward Harrow, Dulwich, Haileybury, North London Collegiate, Marlborough, Shrewsbury, Brighton College, Sherborne, Repton and Wellington - all with overseas branches, variously in Qatar, China, Dubai, Kazakhstan, Bangkok, and South Korea.

This is a latter-day imperialism and can scarcely be a contribution to equity in those countries. I am tempted to say it is “exporting British values” - albeit questionable ones.

A new approach

When, however, I heard the head of one of them boasting that each year he comes to London to interview for new teacher recruits “who have proved themselves in state schools”, I started to wonder about the impact on teacher supply. It isn’t simply public schools that are establishing themselves abroad: there is the Council of British International Schools, which represents over 250 schools.

A friend, in his late thirties and a brilliant history teacher, was lured to teach in Prague. He discovered that the rest of the world knows the quality of our teachers - unlike at home.

All this underlines the need for a new approach to retaining teachers. Here are two suggestions: both will strengthen the new Chartered College of Teaching and focus its main purpose on CPD for teachers.

First, rather like football, levy a “transfer fee” of £20,000 per emigrant teacher from the foreign-based school, and hand the proceeds over to the College.

Second, the government should settle a £300 million one-off endowment on the college with the stipulation that it spends the interest from the invested capital on “professional learning bursaries”. (The precedent for this is Nesta, which has transformed innovation in science, technology and the arts since its foundation in 1998.)

Call them “Greening Bursaries” and provide our secretary of state with a permanent legacy, underlining the importance of teachers to our future wellbeing - and potentially stopping the leakage of teachers to foreign shores.

Sir Tim Brighouse is a former schools commissioner for London